Recent beds for elderly and/or invalid persons are mostly provided with a back lift mechanism that can be driven by an actuator, so that a user can lift the upper half of his body by the back lift mechanism if he has difficulty in lifting the upper half body by himself.
This type of beds includes (1) beds adapted to perform only back lifting operation to lift (incline) the back of the user, (2) beds adapted to simultaneously perform both back lifting operation and knee lifting operation, and (3) beds that utilize a back lift mechanism adapted to perform knee lifting operation first and then back lifting operation, followed by knee lowering operation to lower the knees, in the middle of the back lifting operation, to flatten the knees, before the back is finally lifted (inclined) to a maximum angle of about 70 degrees. See, for example, Japanese Patent Applications Laid Open 2001-29172 (referred to as Patent Document 1), 2004-16558 (Patent Document 2), 2004-16635 (Patent Document 3), and 2004-444 (Patent Document 4).
Beds are often provided on the side frames thereof with side-rails for preventing, for example, the users thereof from falling from the bed, and safety bars for assisting the user to turn out of the bed, as disclosed in Japanese Patent Applications Laid Open 2004-129709 (Patent Document 5) and 2003-52765 (Patent Document 6).
These beds are required to have a structure for suppressing downward slipping of the body of a user caused by a back lifting action and allow the user in a back-lifted condition to sit up on the bedside or turn out of the bed with ease.
However, the mechanism of type (1) mentioned above fails to prevent downward slipping of the body due to the fact that the knees are not lifted in a back lift operation, though it is then easy for him to sit up on the bedside and turn out of the bed when he is in the back-lifted condition. The mechanism of type (2) can prevent downward slipping of the body when the user is in a back-lifted condition by taking advantage of a knee lift mechanism. However, because the mechanism leaves the knees lifted, it forces the user to assume a cramped position under a back-lifted condition, so that the user will have difficulty to sit up on the bedside or turn out of the bed. The mechanism of type (3) also takes advantage of a knee lift mechanism, which, however, forces the user to assume a cramped position up to an intermediate point of the back lifting operation. Further, since the knees are kept lifted at any intermediate inclination angle of the back lift member (the angle referred to as back lift angle) prior to reaching the intermediate point, the user then stays in too unstable a condition to sit up on the bedside or turn out of the bed. In addition, since an appreciably wide region of the bed frame needs to be configured to support knee lifting and leg (calve) lifting actions, it is difficult to effectively cut the weight and cost of the bed. Furthermore, since the knee lifting action is carried out mechanically by the knee lift mechanism that cooperates directly with the rotary members (such as rotary arm 20, leg lift arm 62, and knee lift link 4), forces acting on the links of the rotary members are suddenly reversed near the maximum knee lift angle. As a consequence, small gaps in the rotary members cause irregular motions of the members. A back lift mechanism having such rotary members in direct cooperation with the back lift member requires a bed to have an appropriate height, so that it is difficult to apply it to a low bed.
There is a possibility that some obstacle or a person can accidentally come into a space below a back lift frame. The obstacle or person is then liable to a risk of being trapped under the back lift frame as the back lift frame is returned to an original flat position (in a back-lowering operation). To prevent such trapping of obstacle, a power controller may be used to control the actuator of the back lift mechanism as disclosed in Japanese Patent Application Laid Open 2004-48824 (Patent Document 7), or a limit switch to limit lowering the back lift frame as disclosed in the Patent Document 4 mentioned above. However, such controllers as mentioned above are liable to an erroneous operation or a failure, thereby failing to ensure safety of the beds.
In hospitals and other institutions, beds are generally equipped on the legs thereof with a multiplicity of casters to facilitate transportation of a bed from one room to another. When not in use, the casters are locked by lock mechanisms to make the wheels of the casters not rotatable. To move the bed, the casters are unlocked.
It is necessary to securely fix a bed in a stable condition when the user sits up on the bed or moves from the bed to a wheelchair. To do this, casters having lock mechanisms have been used.
However, since beds are heavy, lock mechanisms for firmly securing casters in a stable condition add to the cost of the casters.
Moreover, since it is necessary to lock multiple casters to fix the bed hazardous bed instability would occur, should one of them were forgotten to be locked.
Regarding this point, Japanese Patent No. 3063392 (Patent Document 8) discloses a bed having legs for fixing the bed and extra legs for adjusting the height of the bed. The extra legs are each provided with casters that can be grounded on the floor in place of the fixed legs when the bed is lifted to a higher level, thereby rendering the bed movable on floor.
Japanese Patent Application Laid Open 2003-237303 (Patent Document 9) discloses a body (bed) which is movable by a multiplicity of casters, the body having: grounding members (legs) underneath the body for immovably supporting the body; and means for changing the height of the wheels of the casters between an “immovable position” at which the lower ends of the wheels are held at the same level as, or higher than, the lowest end of the grounding members, and a “movable position” at which the lower end of the wheels are held lower than that of the grounding members.
However, in the arrangement as described in the Patent Document 8, the casters can be grounded on the floor to make the bed movable while the bed is maintained at a high level, so that the user lying on the moving bed could be scared with a fear of height, and liable to a risk of severe injury such as a bone fracture if the user falls from the bed.
Like the caster locking mechanism mentioned above, the mechanism for grounding the casters (means for changing the height of the wheels of the casters) as described in the Patent Document 9 also adds to the cost of the casters.
The present invention is directed to alleviate the prior art problems as mentioned above, based on the ground that, in order to prevent downward slipping of the body of the user in a back lifting action, it is necessary to lift only the groin sections of thighs and not necessary to lift the knees, as is done by an anchor of a wheelchair. It is, therefore, an object of the invention to provide a bed capable of preventing downward slipping of the body of the user in the back lifting action without forcing him to assume a cramped position, and allowing the user in a back-lifted condition to sit up on, and turn out of, the bed with ease. It is another object of the invention to provide a lightweight and cost effective bed having such capability as stated above.
It is a further object of the invention to provide a bed having a back lift mechanism that is free of irregular movements and applicable to a low bed.
It is a still further object of the invention to provide a bed having a relatively simple mechanism that can secure safeguard against trapping an obstacle in the mechanism.
It is a still further object of the invention to provide a structurally simple and cost effective bed that can be moved by casters without giving the user a fear of height or a risk of causing a serious injury to the user in a fall from the bed, while avoiding a risk of forgetting to lock casters as well as a risk of a fall of the user from the bed trying to move from the bed to a wheelchair or turn out of the bed for example.